HOT-ROLLED AND HEAT TREATED STEEL SHEET AND METHOD FOR ITS MANUFACTURE Russian patent published in 2023 - IPC C21D8/02 C22C38/02 C22C38/04 C22C38/06 C22C38/12 C22C38/14 

FIELD: metallurgy.

SUBSTANCE: hot-rolled and heat-treated steel sheet used in the automotive industry. The sheet is made of steel having a composition comprising in wt.%: С: 0.12-0.25, Mn: 3.0-8.0, Si: 0.7-1.5, Al: 0.3-1.2, V: 0.0002-0.004, S ≤ 0.010, R ≤ 0.020, N ≤ 0.008 and optionally one or more of the following: Mo ≤ 0.5, V ≤ 0.2, Nb ≤ 0.06 and Ti ≤ 0.05, the rest is iron and inevitable impurities resulting from smelting. The sheet has a microstructure consisting in surface fractions of: 5-45% ferrite, 25-85% redistribution martensite, the indicated redistribution martensite has a carbide density of less than 2×10⁶/mm², 10-30% residual austenite, less than 8% fresh martensite. A portion of said fresh martensite is bonded to retained austenite in the form of martensite-austenite (MA) islands with a total surface fraction of less than 10%, and the cake-like index, defined as the ratio of original austenite grain size in the rolling direction (PAGS_roll) to the original austenite grain size in the direction perpendicular to the rolling direction (PAGS_norm), is less than 5.

EFFECT: required mechanical properties and machinability.

10 cl, 5 tbl